Methods and materials to enhance high temperature rheology in invert emulsions

ABSTRACT

An invert emulsion drilling fluid, and a method of drilling with such fluid, having improved rheology at low mud weights and high temperatures. The improved rheology is effected with addition of a rheology additive of the invention comprising fatty dimer diamines or dimer diamines and an organic acid or ester of the acid. A nonlimiting example of such a rheology additive comprises a C36 fatty dimer diamine and adipic acid or dimethyl adipate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to compositions and methods for drilling,cementing and casing boreholes in subterranean formations, particularlyhydrocarbon bearing formations. More particularly, the present inventionrelates to compositions for improving the rheology of invert emulsiondrilling fluids, particularly at high temperatures and pressures.

2. Description of Relevant Art

A drilling fluid or mud is a specially designed fluid that is circulatedthrough a wellbore as the wellbore is being drilled to facilitate thedrilling operation. The various functions of a drilling fluid includeremoving drill cuttings from the wellbore, cooling and lubricating thedrill bit, aiding in support of the drill pipe and drill bit, andproviding a hydrostatic head to maintain the integrity of the wellborewalls and prevent well blowouts.

An important property of the drilling fluid is its rheology, andspecific rheological parameters are intended for drilling andcirculating the fluid through the well bore. The fluid should besufficiently viscous to suspend barite and drilled cuttings and to carrythe cuttings to the well surface. However, the fluid should not be soviscous as to interfere with the drilling operation.

Specific drilling fluid systems are selected to optimize a drillingoperation in accordance with the characteristics of a particulargeological formation. Oil based muds are normally used to drill swellingor sloughing shales, salt, gypsum, anhydrite and other evaporateformations, hydrogen sulfide-containing formations, and hot (greaterthan about 300 degrees Fahrenheit (“° F.”) holes, but may be used inother holes penetrating a subterranean formation as well.

An oil-based invert emulsion-based drilling fluid may commonly comprisebetween about 50:50 to about 95:5 by volume oil phase to water phase.Such oil-based muds used in drilling typically comprise: a base oilcomprising the external phase of an invert emulsion; a saline, aqueoussolution (typically a solution comprising about 30% calcium chloride)comprising the internal phase of the invert emulsion; emulsifiers at theinterface of the internal and external phases; and other agents oradditives for suspension, weight or density, oil-wetting, fluid loss orfiltration control, and rheology control. In the past, such additivescommonly included organophilic clays and organophilic lignites. See H.C. H. Darley and George R. Gray, Composition and Properties of Drillingand Completion Fluids 66-67, 561-562 (5^(th) ed. 1988). However, recenttechnology as described for example in U.S. Pat. Nos. 7,462,580 and7,488,704 to Kirsner, et al., introduced “clay-free” invertemulsion-based drilling fluids, which offer significant advantages overdrilling fluids containing organophilic clays.

As used herein and for the purposes of the present invention, the term“clay-free” (or “clayless) means a drilling fluid made without additionof any organophilic clays or organophilic lignites to the drilling fluidcomposition. During drilling, such “clay-free” drilling fluids mayacquire clays and/or lignites from the formation or from mixing withrecycled fluids containing clays and/or lignites. However, suchcontamination of “clay-free” drilling fluids is preferably avoided andorganophilic clays and organophilic lignites should not be deliberatelyadded to “clay-free” drilling fluids during drilling.

Invert emulsion-based muds or drilling fluids (also called invertdrilling muds or invert muds or fluids) comprise a key segment of thedrilling fluids industry, and “clay-free” invert emulsion-based muds,particularly those capable of “fragile gel” behavior as described inU.S. Pat. Nos. 7,462,580 and 7,488,704 to Kirsner, et al., are becomingincreasingly popular.

Clay-free invert emulsion drilling fluids, like INNOVERT® drilling fluidavailable from Halliburton Energy Services, Inc., in Duncan, Okla. andHouston, Tex., for example, have been shown to yield high performance indrilling, with “fragile gel” strengths and rheology leading to lowerequivalent circulating density (ECDs) and improved rate of penetrationROP.

A limiting factor in drilling a particular portion of a well is the mudweight (density of the drilling fluid) that can be used. If too high amud weight is used, fractures are created in the formation withresulting loss of drilling fluid and other operating problems. If toolow a mud weight is used, formation fluids can encroach into the well,borehole collapse may occur due to insufficient hydrostatic support, andin extreme cases safety can be compromised due to the possibility of awell blowout. Many times, wells are drilled through weak orlost-circulation-prone zones prior to reaching a potential producingzone, requiring use of a low mud weight and installation of sequentialcasing strings to protect weaker zones above the potential producingzone. A particularly critical drilling scenario is one that combinesdeepwater and shallow overburden, as is typical of ultra deepwaterfields in Brazil. This scenario is characterized by high pore fluidpressure, low effective stresses, low fracturing gradients and narrowmud weight windows.

Commercially available clay-free invert emulsion drilling fluids mayhave less than preferred rheology at low mud weights, that is, mudweights ranging from about 9 ppg to about 12 ppg, with temperatures upto about 375° F. or higher. Addition of inert solids may improve therheology, but result in a decreased rate of penetration during drillingand loss of or decline in other benefits seen with a clay free system.Such inert solids include for example, fine sized calcium carbonate, andthe term as used herein is not meant to be understood to include orrefer to drill cuttings. Low mud weight or reduced density clay-free oilbased invert emulsion drilling fluids also may show a decline in thedesired “fragile gel” strength characteristic of clay-free invertemulsion drilling fluids. “Fragile gel” strength generally refers to theability of the drilling fluid to both suspend drill cuttings at rest andshow a lack of a pressure spike upon resumption of drilling. Solidsadded to an invert emulsion drilling fluid may be difficult to removelater in the drilling process and can ultimately lead to poor controlover the rheology of the drilling fluid system and decreased rate ofpenetration (ROP).

Also, commonly used mineral oils often used in formulating invertemulsion fluids include n-paraffins, mixtures of n-paraffins,iso-paraffins, and cyclic and branched chain alkanes. These base oilshave low viscosities and invert emulsion fluids prepared with themtypically need additives to impart adequate rheology.

Increasingly invert emulsion-based drilling fluids are being subjectedto ever greater performance and cost demands as well as environmentalrestrictions. Consequently, there is a continuing need and industry-wideinterest in new drilling fluids that provide improved performance whilestill affording environmental and economical acceptance.

SUMMARY OF THE INVENTION

The present invention provides an additive for oil-based invert emulsiondrilling fluids to improve the rheology of the fluids without theaddition of inert solids, across a broad range of temperatures andpressures. The invention is particularly advantageous at hightemperatures and pressures, such as temperatures ranging from about 100°F. to about 375° F. or higher and pressures ranging from about 14 psi toabout 30,000 psi or higher. The additive of the invention comprises ahydrophobic amine and an organic acid or its corresponding ester,wherein the hydrophobic amine has the following general structure:

where R is a hydrophobic or partially hydrophobic group with carbonatoms ranging from about 16 to about 54, straight chained or branched,and aliphatic, cycloaliphatic or aryl aliphatic; N is a primary,secondary or tertiary amine wherein the R1 and R2 groups may be the sameor different and are selected from the group consisting of a hydrogengroup, alkyl group, cyano alkyl group, amino alkyl group, aryl group,amino aryl group, hydroxyl alkyl group or a derivative thereof;alternatively the R1 and R2 can be a carbonyl group, carbonate group,alkoxy group, hydroxyl group or a derivative thereof; X comprises ahydrophilic group such as an amine which can be primary, secondary ortertiary with substituents being a hydrogen group, alkyl group, cyanoalkyl group, amino alkyl group, amino aryl group, hydroxyl alkyl groupor a derivative thereof; alternatively the X group can be an amidegroup, amine oxide group, betaine group, ester group, carboxylic acidgroup, ether group, hydroxyl group, phosphate group, phosphonate group,pyrrolidone group, haloformyl group, nitrate group, nitrite group,sulfate group, sulfonate group, imidazoline group, pyridine group, sugargroup, or a combination or derivative thereof; and wherein the organicacid is a carboxylic acid with at least one COOH group, where thesolubility of the organic acid in water is at least 0.1% w/w in water at20° C.

An example commercially available dimer diamine suitable for use in theadditive of the invention is a C36 dimer diamine containing C18 fattymonoamine and C54 fatty trimer triamine which are obtained during thecommercial production of the dimer diamine. Generally, quantities ofsuch hydrophobic amine ranging from about 0.1 ppb to about 20 ppb arepreferred and are effective even when the mud weight is low, that is, isin the range of about 9 to about 12 ppg. With this amine, generallyquantities of 0.1 ppb to about 20 ppb of the organic acid or estercorresponding to the organic acid are used. Examples of commerciallyavailable organic acids suitable for use in the additive of theinvention include lactic acid, formic acid, acrylic acid, acetic acid,chloroacetic acid, dichloroacetic acid, trichloroacetic acid,trifluoroacetic acid, propanoic acid, butyric acid, pentanoic acid,hexanoic acid, heptanoic acid, oxalic acid, malonic acid, succinic acid,glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid,sebacic acid, maleic acid, fumaric acid, aspartic acid, citric acid,isocitric acid, aconitic acid, tartaric acid, benzoic acid, p-aminobenzoic acid, phthalic acid, terephthalic acid, trimesic acid, withoutlimitation.

The additive of the present invention is also particularly useful informulating oil-based invert emulsion fluids with improved rheology,even when the fluids have a low mud weight. Thus, the present inventionalso provides improved oil-based invert emulsion drilling fluids andimproved methods of drilling wellbores in subterranean formationsemploying such oil-based invert emulsion muds or drilling fluids, evenwhen the muds have low mud weight. As used herein, the term “drilling”or “drilling wellbores” shall be understood in the broader sense ofdrilling operations, which include running casing and cementing as wellas drilling, unless specifically indicated otherwise.

The invert emulsion drilling fluid of the present invention, or used inmethods of the present invention, comprises an oil:water ratiopreferably in the range of 50:50 to 95:5 and preferably employs anatural oil, such as for example without limitation diesel oil ormineral oil, or a synthetic base, as the oil phase, and water comprisinga salt such as calcium chloride for example as the aqueous phase. Therheology additive of the invention is included for rheology stability.Clay and/or inert solids are preferably not added to provide weight orrheology control to the fluid. Invert emulsion drilling fluids of theinvention may also demonstrate “fragile gel” behavior when the drillingfluid is “clay-free.”

Addition of the rheology additive of the invention to the invertemulsion drilling fluid increases the Low Shear Yield Point (LSYP),Yield Point (YP), and the 10 minute Gel Strength but limits the increasein the Plastic Viscosity (PV) to about 50% or less, relative to thedrilling fluid not having the additive, when measured at 120° F. At HighPressure High Temperature (HPHT) conditions, the invert emulsiondrilling fluid of the present invention comprising the rheology additiveof the invention has increased LSYP, YP, and 10 minute Gel Strength butsimilar or lower PV, relative to the drilling fluid without the rheologyadditive of the invention. Such a similar or lower PV seen with theinvert emulsion drilling fluid of the invention is believed to helpminimize the amount of density increase caused by pumping of the fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph comparing the plastic viscosity, yield point and lowshear yield point of an example 12 ppg drilling fluid formulation of theinvention comprising a dimethyl adipate-fatty dimer diamine rheologyadditive of the invention, under various temperature and pressureconditions.

FIG. 2 is a graph comparing the plastic viscosity, yield point and lowshear yield point of a different example 12 ppg drilling fluidformulation of the invention comprising an adipic acid-fatty dimerdiamine rheology additive of the invention, under various temperatureand pressure conditions.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides a rheology additive for oil-based, invertemulsion drilling fluids which imparts to such drilling fluidscomprising such additive improved performance in the field at mudweights in the range of about 9 ppg to about 20 ppg. The presentinvention also provides a method of drilling employing an invertemulsion drilling fluid of the invention or an invert emulsion drillingfluid comprising the rheology additive of the invention.

The oil base of invert emulsion drilling fluids of the present inventionmay be a natural oil such as for example mineral oil or diesel oil, or asynthetic base such as, for example, BAROID ALKANE® base available fromHalliburton Energy Services, Inc., in Houston, Tex. and Duncan, Okla.,and EDC 99DW base available from TOTAL. A mineral oil may besuccessfully used as the oil base in the present invention, even thoughin the prior art some difficulties have been experienced in obtainingdesirable rheological properties with mineral oils under certainconditions such as low mud weights, that is, mud weights ranging fromabout 9 to about 12 ppg, and particularly at high temperatures (greaterthan 225° F.). Mineral oils particularly suitable for use in theinvention are selected from the group consisting of n-paraffins,iso-paraffins, cyclic alkanes, branched alkanes, and mixtures thereof.

An aqueous solution containing a water activity lowering compound,composition or material, comprises the internal phase of the invertemulsion. Such solution is preferably a saline solution comprisingcalcium chloride (typically about 25% to about 30%, depending on thesubterranean formation water salinity or activity), although other saltsor water activity lowering materials such as for example sugar known inthe art may alternatively or additionally be used. Such other salts mayinclude for example sodium chloride, sodium bromide, calcium bromide andformate salts. Water preferably comprises less than 50%, or as much asabout 50%, of the drilling fluid and the oil:water ratio preferablyranges from about 50:50 to about 95:5.

Drilling fluids of the present invention uniquely include the additiveof the present invention as a rheology modifier, as will be discussedfurther below. Further, the drilling fluids of, or for use in, thepresent invention, have added to them or mixed with their invertemulsion oil base, other fluids or materials needed to comprise completedrilling fluids. Such other materials optionally may include, forexample: additives to reduce or control low temperature rheology or toprovide thinning, for example, additives having the trade namesCOLDTROL®, ATC®, and OMC2™; additives for enhancing viscosity, forexample, an additive having the trade name RHEMOD L™ (modified fattyacid); additives for providing temporary increased viscosity forshipping (transport to the well site) and for use in sweeps, forexample, an additive having the trade name TEMPERUS™ (modified fattyacid); additives for filtration control, for example, additives havingthe trade names ADAPTA® and BDF-366; an emulsifier activator, such as,for example, lime; additives for high temperature high pressure control(HTHP) and emulsion stability, for example, an additive having the tradename FACTANT™ (highly concentrated tall oil derivative); and additivesfor emulsification, for example, an additive having the trade name EZMUL® NT (polyaminated fatty acid). All of the aforementioned trademarkedproducts are available from Halliburton Energy Services, Inc. inHouston, Tex., and Duncan, Okla., U.S.A. As with all drilling fluids,the exact formulations of the fluids of the invention vary with theparticular requirements of the subterranean formation.

A preferred commercially available drilling fluid system for use in theinvention is the INNOVERT® drilling fluid system, having aparaffin/mineral oil base, available from Baroid, a Halliburton Company,in Houston, Tex. and Duncan, Okla. The INNOVERT® drilling fluid systemtypically comprises the following additives, in addition to theparaffin/mineral oil base and brine, for use as an invert emulsiondrilling fluid: RHEMOD™ L modified fatty acid suspension andviscosifying agent, BDF-366™ or ADAPTA™ copolymer for HPHT filtrationcontrol, particularly for use at high temperatures, and EZ MUL® NTpolyaminated fatty acid emulsifier/oil wetting agent, also particularlyfor use at high temperatures. Commercially available INNOVERT® drillingfluid systems also typically include TAU-MOD™ amorphous/fibrous materialas a viscosifier and suspension agent. However, with the presentinvention, where the drilling fluid system has uniquely added thereto ahydrophobic amine and organic acid additive as a rheology modifier,TAU-MOD™ material is optional.

Invert emulsion drilling fluids of the present invention, comprising theadditive of the invention, maintain acceptable and even preferredrheology measurements at low mud weights and do not experience adecreased rate of penetration (and with clay-free invert emulsiondrilling fluids, also do not experience a decline in desired fragile gelstrength) when in use in drilling even at high temperatures andpressures. At HPHT conditions, the invert emulsion drilling fluids ofthe present invention, comprising the hydrophobic amine and organic acidadditive of the invention, has increased LSYP, YP, and 10 minute GelStrength but similar PV relative to the drilling fluid without theadditive of the invention. These advantages of the present invention arebelieved to be due to the addition of the additive of the invention tothe drilling fluid. The advantages of the present invention areespecially appreciated where the drilling fluid does not also containorganophilic clay or lignite.

The additive of the invention comprises a dimer diamine or fatty dimerdiamine and an organic acid or an ester corresponding to the organicacid, where the organic acid is a carboxylic acid with at least one COOHgroup and has a solubility of at least 0.1% w/w in water at 20° C.Examples of commercially available organic acids suitable for use in theadditive of the invention include lactic acid, formic acid, acrylicacid, acetic acid, chloroacetic acid, dichloroacetic acid,trichloroacetic acid, trifluoroacetic acid, propanoic acid, butyricacid, pentanoic acid, hexanoic acid, heptanoic acid, oxalic acid,malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid,suberic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid,aspartic acid, citric acid, isocitric acid, aconitic acid, tartaricacid, benzoic acid, p-amino benzoic acid, phthalic acid, terephthalicacid, trimesic acid, without limitation

Preferred commercially available fatty dimer diamines that may be usedin the additive of the invention include for non-limiting exampleVERSAMINE® 552 hydrogenated fatty C36 dimer diamine, and VERSAMINE® 551fatty C36 dimer diamine, both available from Cognis Corporation(functional products) of Monheim, Germany and Cincinnati, Ohio andPRIAMINE™ 1073 and PRIAMINE™ 1074 fatty C36 dimer diamine, bothavailable from Croda Internationale Plc of Goole East Yorkshire, UnitedKingdom and New Castle, Del. Typically, an amount of such dimer diaminein the range of about 0.1 pound per barrel (ppb) to about 20 ppb issufficient for purposes of the invention. These fatty dimer diamines areprepared commercially from fatty dimer diacids which have been producedfrom dimerisation of vegetable oleic acid or tall oil fatty acid bythermal or acid catalyzed methods.

The dimerisation of C18 tall oil fatty acids produces the materialleading to the C36 dimer acids. This material is a mixture of monocyclicdicarboxylic acid, acyclic dicarboxylic acid and bicyclic dicarboxylicacid along with small quantities of trimeric triacids. These diacids areconverted into diamines via the reaction scheme given below:

These diamines are further converted into compounds that fall under thescope of hydrophobic amine additives. These diamines are converted intocyanoethyl derivatives via cyanoethylation with acrylonitrile; thesecyanoethyl derivatives are further reduced into aminopropyl amines viareduction as shown in the reaction scheme II below, as taught in U.S.Pat. No. 4,250,045, issued Feb. 10, 1981 to Coupland, et al.

Dicyanoethylated dimer diamine is available commercially as Kemamine DC3680 and 3695 and di N-aminopropylated dimer diamine is availablecommercially as Kemamine DD 3680 and 3695 from Chemtura Corporation USA.Different structures of the dimeric hydrophobic amine additives aregiven below:

Laboratory tests demonstrate the effectiveness of the present invention.Referring to experiments whose results are graphed in FIG. 1, a 12 ppgINNOVERT® invert emulsion drilling fluid was prepared usingparaffin/mineral oil base in a 70:30 oil to water ratio with calciumchloride brine having a water phase salinity of 250,000 parts permillion (ppm). To this, additives were mixed in for a drilling fluidhaving the components as indicated in Table 1 below:

TABLE 1 Effect of Adipic Acid/Fatty Dimer Diamine and DimethylAdipate/Fatty Dimer Diamine Additives on Rheology of 12 ppg InvertEmulsion Drilling Fluids Time, 1 OWR 70:30 min (Base) 2 3 4 EDC 99-DW ®,ppb 150.6 147.0 149.7 148.8 EZ MUL NT ®, ppb 5 11 11 11 11 Lime, ppb 51.3 1.3 1.3 1.3 ADAPTA ®, ppb 5 2 2 2 2 Dimethyl Adipate, ppb 5 — 5 — —Adipic acid, ppb 5 — — 2.5 5 CaCl₂ soln (250K ppm), ppb 5 113.7 113.8113.1 112.5 Revdust, ppb 5 20 20 20 20 BDF 570 ™ Fatty Dimer 5 2 2 2 2Diamine, ppb BAROID ® Barite, ppb 5 203.3 201.9 202.4 201.4 Hot rolledat 250 F., 16 hrs 600 rpm @ 120 F. 60 89 128 152 300 rpm @ 120 F. 32 6090 120 200 rpm @ 120 F. 24 49 74 108 100 rpm @ 120 F. 15 35 57 97  6 rpm@ 120 F. 5 16 28 93  3 rpm @ 120 F. 4 15 26 80 PV @ 120 F. 28 29 38 32YP @ 120 F. 4 31 52 88 LSYP @ 120 F. 3 14 24 67 10 sec gel @ 120 F. 6 2130 82 10 min gel @ 120 F. 9 26 40 85All trademarked products above and in other tables below are availablefrom Halliburton Energy Services, Inc., in Houston, Tex. and Duncan,Okla., except that REV DUST is an artificial drill solid available fromMilwhite Inc, in Houston Tex. These compositions set forth in Table 1were hot rolled at 250° F. for 16 hours. The fluids were then furthermixed for 5 minutes and evaluated on a FANN 35 rheometer at 120° F.,testing Plastic Viscosity (PV), Yield Point (YP), yield stress (Tauzero) and Low Shear Yield Point (LSYP).

The Plastic Viscosity (PV), Yield Point (YP), Yield Stress (Tau zero)and Low Shear Yield Point (LSYP) of the invert emulsion drilling fluidwere determined on a direct-indicating rheometer, a FANN 35 rheometer,powered by an electric motor. The rheometer consists of two concentriccylinders, the inner cylinder is called a bob, while the outer cylinderis called a rotor sleeve. The drilling fluid sample is placed in athermostatically controlled cup and the temperature of the fluid isadjusted to 120 (±2)° F. The drilling fluid in the thermostaticallycontrolled cup is then placed in the annular space between the twoconcentric cylinders of the FANN 35. The outer cylinder or rotor sleeveis driven at a constant rotational velocity. The rotation of the rotorsleeve in the fluid produces a torque on the inner cylinder or bob. Atorsion spring restrains the movement of the bob, and a dial attached tothe bob indicates displacement of the bob. The dial readings aremeasured at different rotor sleeve speeds of 3, 6, 100, 200, 300 and 600revolutions per minute (rpm).

Generally, Yield Point (YP) is defined as the value obtained from theBingham-Plastic rheological model when extrapolated to a shear rate ofzero. It may be calculated using 300 rpm and 600 rpm shear rate readingsas noted above on a standard oilfield rheometer, such as a FANN 35 or aFANN 75 rheometer. Similarly, Yield Stress or Tau zero is the stressthat must be applied to a material to make it begin to flow (or yield),and may commonly be calculated from rheometer readings measured at ratesof 3, 6, 100, 200, 300 and 600 rpm. The extrapolation may be performedby applying a least-squares fit or curve fit to the Herchel-Bulkleyrheological model. A more convenient means of estimating the YieldStress is by calculating the Low-Shear Yield Point (LSYP) by the formulashown below in Equation 2 except with the 6 rpm and 3 rpm readingssubstituted for the 600-rpm and 300-rpm readings, respectively. PlasticViscosity (PV) is obtained from the Bingham-Plastic rheological modeland represents the viscosity of a fluid when extrapolated to infiniteshear rate. The PV is obtained from the 600 rpm and the 300 rpm readingsas given below in Equation 1. A low PV may indicate that a fluid iscapable of being used in rapid drilling because, among other things, thefluid has low viscosity upon exiting the drill bit and has an increasedflow rate. A high PV may be caused by a viscous base fluid, excesscolloidal solids, or both. The PV and YP are calculated by the followingset of equations:PV=(600 rpm reading)−(300 rpm reading)  (Equation 1)YP=(300 rpm reading)−PV  (Equation 2)More particularly, each of these tests were conducted in accordance withstandard procedures set forth in Recommended Practice 13B-2, RecommendedPractice for Field Testing of Oil-based Drilling Fluids, Fourth Edition,American Petroleum Institute, Mar. 1, 2005, the contents of which ishereby incorporated herein by reference.

The results of the tests reported in Table 1 demonstrate that the baseformulation of the invert emulsion drilling fluid had a Yield Point (YP)of 4 and a Low-Shear Yield Point (LSYP) of 3. However, on addition ofthe adipic acid (HOOC—(CH₂)₄—COOH) at 2.5 ppb concentration to the baseformulation of the invert emulsion drilling fluid, the fluid's YP andLSYP improved significantly—by 1200% for the YP and 700% for the LSYP.On adding a higher concentration of adipic acid—5 ppb concentration—tothe base fluid, the fluid's YP and LSYP improved even more—by 2100% forthe YP and 675% for the LSYP. Addition of dimethyl adipate(H₃COOC—(CH₂)₄—COOCH₃) at 5 ppb concentration to the base formulation ofthe invert emulsion drilling fluid, also improved the fluid's YP andLSYP—by 675% for the YP and 370% for the LSYP. The PV increased onlymarginally, with the highest rise being 35% for 2.5 ppb adipic acid.

Samples of formulations 2 and 3 of the invert emulsion drilling fluidset forth in Table 1, containing respectively 5 ppb dimethyl adipate and2 ppb fatty dimer diamine (formulation 2) and 2.5 ppb adipic acid and 2ppb fatty dimer diamine (formulation 3), were evaluated further with aFANN 75 rheometer using simulated down hole conditions, and particularlytesting high temperature and high pressure rheology. The FANN 75rheometer measures similarly as the FANN 35 rheometer but can measurerheology under high temperature and pressure. The results of these testsare set forth in Tables 2 and 3 (showing rheological data) and in FIGS.1 and 2 (showing PV, YP and LSYP).

TABLE 2 Fann75 Rheology of 12 ppg Invert Emulsion Drilling Fluid withDimethyl Adipate/Fatty Dimer Diamine Additive Under High Temperature andHigh Pressure Conditions 120 F. 150 F. 175 F. 200 F. 225 F. 250 F. 275F. 300 F. RPM 0 psi 3000 psi 4500 psi 6000 psi 7500 psi 9000 psi 10500psi 12000 psi 600 82 85 83 81 84 85 85 83 300 56 58 57 56 61 62 62 60200 47 48 47 48 53 54 53 51 100 36 37 37 38 43 43 42 40  6 19 23 23 2224 24 21 20  3 19 23 22 21 22 22 19 19 PV 26 27 26 25 23 23 23 23 YP 3031 31 31 38 39 39 37 LSYP 19 23 21 20 20 20 17 18

TABLE 3 Fann75 Rheology of 12 ppg Invert Emulsion Drilling Fluid withAdipic Acid/Fatty Dimer Diamine Additive Under High Temperature and HighPressure Conditions 120 F. 150 F. 175 F. 200 F. 225 F. RPM 0 psi 3000psi 4500 psi 6000 psi 7500 psi 600 127 131 127 114 110 300 87 90 87 7978 200 73 74 71 67 67 100 56 58 56 54 54  6 30 37 38 35 33  3 30 36 3633 32 PV 40 41 40 35 32 YP 47 49 47 44 46 LSYP 30 35 34 31 31

The rheology additive of the invention was also tested in 12 ppg invertemulsion drilling fluids prepared with different mineral oil bases andin the absence of any externally added low gravity solids (LGS). Thecompositions and results of these tests are shown in Table 4. Again, theadditive of the invention resulted in the drilling fluids showingsignificant improvements in YP and LSYP, with the respective rise being2100% for YP and 4260% for LSYP for the ESCAID 110 oil based invertemulsion fluid, and 300% for YP and 510% for LSYP for the Baroid Alkaneoil based invert emulsion fluid. The PV changed only marginally incomparison to the YP and the LSYP for these mineral oils.

TABLE 4 Performance of Adipic Acid/Fatty Dimer Diamine and DimethylAdipate/Fatty Dimer Diamine Additives in 12 ppg Invert Emulsion DrillingFluids Having Different Mineral Oil Bases Time, 1 3 5 OWR 70:30 min(BASE) 2 (BASE) 4 (BASE) 6 EDC 99-DW ®, ppb 150.6 148.8 — — — — Escaid110, ppb — — 146.29 144.54 — — Baroid Alkane, ppb — — — — 144.16 143.29EZ MUL NT ®, ppb 2 11 11 11 11 11 11 Lime, ppb 5 1.3 1.3 1.3 1.3 1.3 1.3ADAPTA ®, ppb 5 2 2 2 2 2 2 Adipic acid, ppb 5 — 5 — 5 — 2.5 CaCl₂soln(250K ppm), ppb 5 113.7 112.5 113.27 112.01 113.06 112.43 Revdust,ppb 5 20 20 20 20 20 20 BAROID ®, ppb 5 203.3 201.4 208.1 206.1 210.5209.5 Fatty Dimer Diamine, ppb 5 2 2 2 2 2 2 Hot rolled at 250 F., 16hrs 600 rpm @ 120 F. 60 152 45 161 55 132 300 rpm @ 120 F. 32 120 25 13737 103 200 rpm @ 120 F. 24 108 17 125 30 87 100 rpm @ 120 F. 15 97 11114 21 73  6 rpm @ 120 F. 5 93 3 104 8 45  3 rpm @ 120 F. 4 80 3 102 741 PV @ 120 F. 28 32 20 24 18 29 YP @ 120 F. 4 88 5 113 19 74 LSYP @ 120F. 3 67 3 101 6 37 10 sec gel @ 120 F. 6 82 3 101 7 40 10 min gel @ 120F. 9 85 6 106 10 46

The rheology additive of the present invention has the further advantageof being biodegradable with low ecotoxicity. Specifically, testing in abioassay lab at Houston, Tex. indicated that fatty dimer diamines arebiodegradable (66.5% and 82.1% in 28 days and 35 days respectively,marine BODIS method) and have low ecotoxicity (48-hr LC50 of >10 g/L,96-hr LC50 of >10 g/L and a 96-hr NOEC of 10 g/L to the marine juvenilefish Cyprinodont variegates; 24-hr LC50, 48-hr LC50, 48-hr LC90 of >10g/L and a 48-hr NOEC of 10 g/L for marine copepod Acartia Tonsa, a 10day LC50 value of greater than 12469.47 mg.kg-1 (via dried sediment) tothe marine amphipod Corophium volutator in the sediment phase). The testmethods for Cyprinodon variegatus fish were consistent with OECD 203guideline for marine testing of offshore chemicals. The test methods forcopepods Acartia Tonsa were consistent with ISO 14669:1999(E) guidelinefor marine testing of offshore chemicals while the test methods foralgae Skeletonema costatum were consistent with ISO 10253:2006, OECDguideline as adapted for marine testing of offshore chemicals. Also,dimethyl adipate is reported as readily biodegradable (seehttp://www.dow.com/custproc/products/dma.htm) and adipic acid isreported as readily biodegradable (seehttp://fscimage.fishersci.com/msds/00390.htm). An 84% conversion ofadipic acid's carbon content to carbon dioxide was observed after 30days aerobic incubation in soil biometer flasks at an initial adipicacid concentration of 1 mg/g soil. Also, an estimated BCF value of 0.68for adipic acid, from a measured log Kow, suggests that bioconcentrationin aquatic organisms is low. Eco-toxicity study of adipic acid shows aLC50 value of 97-330 mg/L (24-96 Hr.; Static conditions, 18-22° C.) forBluegill/Sunfish. In the case of dimethyl adipate too, thebioconcentration potential is low (BCF<100 or Log Pow<3). Aneco-toxicity study of Dimethyl Adipate indicated a LC50 value of 72 mg/land EC50 value of >100 mg/lit for water flea Daphnia magna, (static, 48hr.) and green alga Selenastrum capricornutum (Growth rate inhibition,72 h) respectively. Due to the high biodegradability, lowbioaccumulation potential and low ecotoxicity, the additives dimethyladipate and adipic acid are believed likely to pass even stringent NorthSea regulations.

The advantages of the methods of the invention may be obtained byemploying a drilling fluid of the invention in drilling operations. Thedrilling operations—whether drilling a vertical or directional orhorizontal borehole, conducting a sweep, or running casing andcementing—may be conducted as known to those skilled in the art withother drilling fluids. That is, a drilling fluid of the invention isprepared or obtained and circulated through a wellbore as the wellboreis being drilled (or swept or cemented and cased) to facilitate thedrilling operation. The drilling fluid removes drill cuttings from thewellbore, cools and lubricates the drill bit, aids in support of thedrill pipe and drill bit, and provides a hydrostatic head to maintainthe integrity of the wellbore walls and prevent well blowouts. Thespecific formulation of the drilling fluid in accordance with thepresent invention is optimized for the particular drilling operation andfor the particular subterranean formation characteristics and conditions(such as temperatures). For example, the fluid is weighted asappropriate for the formation pressures and thinned as appropriate forthe formation temperatures. The fluids of the invention afford real-timemonitoring and rapid adjustment of the fluid to accommodate changes insuch subterranean formation conditions. Further, the fluids of theinvention may be recycled during a drilling operation such that fluidscirculated in a wellbore may be recirculated in the wellbore afterreturning to the surface for removal of drill cuttings for example. Thedrilling fluid of the invention may even be selected for use in adrilling operation to reduce loss of drilling mud during the drillingoperation and/or to comply with environmental regulations governingdrilling operations in a particular subterranean formation.

The foregoing description of the invention is intended to be adescription of preferred embodiments. Various changes in the details ofthe described fluids and methods of use can be made without departingfrom the intended scope of this invention as defined by the appendedclaims.

What is claimed is:
 1. A method for drilling in a subterranean formationcomprising providing or using in the drilling an invert emulsiondrilling fluid having an a. oleaginous continuous phase, b. anon-oleaginous discontinuous phase, and a c. rheology additivecomprising a i. fatty dimer diamine and ii. an organic acid orcorresponding ester of the organic acid or combinations thereof, whereinthe organic acid is selected from the group consisting of: lactic acid,formic acid, acrylic acid, acetic acid, chloroacetic acid,dichloroacetic acid, trichloroacetic acid, trifluoroacetic acid,propanoic acid, butyric acid, pentanoic acid, hexanoic acid, heptanoicacid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipicacid, pimelic acid, suberic acid, azelaic acid, sebacic acid, maleicacid, fumaric acid, aspartic acid, citric acid, isocitric acid, aconiticacid, tartaric acid, benzoic acid, p-amino benzoic acid, phthalic acid,terephthalic acid, and trimesic acid.
 2. The method of claim 1 whereinthe drilling fluid with the additive, when compared to the drillingfluid without the additive, restricts the increase in plastic viscosityto 50% or less and has a characteristic selected from the groupconsisting of: an increased yield point; an increased low shear yieldpoint; an increased gel strength; and any combination thereof.
 3. Themethod of claim 1 wherein the organic acid has at least 0.1% w/wsolubility in water at 20° C.
 4. The method of claim 1 wherein thedrilling fluid is organoclay-free.
 5. The method of claim 1 wherein theoleaginous phase comprises: a synthetic oil comprising an ester orolefin; a diesel oil; or a mineral oil selected from the groupconsisting of n-paraffins, iso-paraffins, cyclic alkanes, branchedalkanes, and mixtures thereof.
 6. The method of claim 1 wherein thedrilling fluid has mud weight in the range of about 9 to 20 ppg.
 7. Themethod of claim 1 wherein the drilling fluid comprises from about 0.1ppb to about 40 ppb of the rheology additive.
 8. The method of claim 1wherein the rheology additive comprises from about 0.1 ppb to about 20ppb of the amine and 0.1 ppb to about 20 ppb of the acid or ester. 9.The method of claim 1 wherein the drilling fluid has an oil:water ratioin the range of about 50:50 to about 95:5.
 10. The method of claim 1wherein the non-oleaginous continuous phase contains a water activitylowering material selected from the group consisting of: sugar; saltsselected from the group consisting of calcium chloride, calcium bromide,sodium chloride, sodium bromide, and formate; and combinations thereof.11. The method of claim 1 wherein the drilling fluid with the rheologyadditive, when compared to the drilling fluid without the rheologyadditive, has a lower HPHT fluid loss.
 12. The method of claim 1 whereinthe drilling fluid with the rheology additive, under HPHT conditions,has enhanced YP, LSYP and gel strength but similar PV, when compared tothe drilling fluid without the rheology additive.
 13. The method ofclaim 1 where the invert emulsion fluid comprises at least one additivefrom the group consisting of: weighting agents, inert solids, fluid losscontrol agents, emulsifiers, salts, dispersion aids, corrosioninhibitors, emulsion thinners, emulsion thickeners, viscosifier, HPHTemulsifier-filtration control agents, and any combination thereof. 14.The method of claim 1 further comprising drilling, running casing and/orcementing a wellbore in the subterranean formation.
 15. A method fordrilling in a high temperature subterranean formation comprisingproviding or using in the drilling an invert emulsion drilling fluidhaving a mud weight in the range of about 9 ppg to about 20 ppg, whereinthe drilling fluid comprises a continuous oleaginous phase and adiscontinuous non-oleaginous phase in an oil:water ratio in the range ofabout 50:50 to about 95:5, and 0.1 ppb to 40 ppb rheology additivecomprising a 36 carbon fatty dimer diamine with the molecular structure:

and an organic acid or its corresponding ester which are adipic acid anddimethyl adipate, wherein the drilling fluid with the rheology additive,when compared to the drilling fluid without the rheology additive,restricts the increase in plastic viscosity to 60% or less and has acharacteristic selected from the group consisting of: an increased yieldpoint; an increased low shear yield point; an increased gel strength;and any combination thereof.
 16. The method of claim 15 wherein thedrilling fluid has an oleaginous phase selected from the group of oilsconsisting of: diesel oils; ester oils; olefins; and mineral oilsselected from the group consisting of n-paraffins, iso-paraffins, cyclicalkanes, branched alkanes, and mixtures thereof.
 17. The method of claim15 wherein the rheology additive is biodegradable.